The present invention refers to a heat exchanger plate for a plate heat exchanger, wherein the plate includes at least a first area with a corrugation of ridges and valleys, the plurality of which extends in a first direction, wherein the plate has a central rotary axis which extends in parallel with a normal line of the plate. The invention also refers to a plate package for a plate heat exchanger, and a plate heat exchanger.
Such heat exchanger plates for rotation a quarter of a round are known from EP-A-165 179. The plates have a substantially square shape and form a plate package where the inlets and the outlets extend through the sides of the plate package, i. e. the heat exchanger media flow into and out of the plate package in a direction which is substantially parallel to the main extension plane of the plates. Each plate has four side edges, wherein two opposite side edges are folded downwardly and the two other opposite side edges are folded upwardly. Every second plate is rotated 90° in the plate package, wherein the downwardly folded side edges of a plate abut the upwardly folded side edges of an adjacent plate, wherein these side edges are connected to each other by means of a weld joint. In each corner of each plate a tab is formed, which extends along a diagonal direction and in a plane that is substantially perpendicular to the extension plane of the plates.
The plates disclosed in EP-A-165 179 have an active heat exchanging surface with a corrugation of ridges and valleys, which extend in a diagonal direction that is inclined 45° to the side edges of the plates. Due to reasons of the manufacturing technology, a corrugation may not extend to the side edges but there has to be an edge area in order to enable, for instance, bending of the edge. The edge area may in principle be only a substantially line-shaped bending area but preferably the edge area has a substantially plane surface that has a width of 10–15 mm. By such a corrugation the plate becomes very rigid with regard to the shape in the diagonal direction, in which the ridges and the valleys extend, but is significantly less rigid transversely to the corrugation.
The plates are manufactured by compression moulding and when the plates are compressed for the shaping of the pattern, the material is extended transversally to the corrugation. When the press tool then is open and the plate is released, a certain backspring is obtained due to the elasticity of the material. Since the main backspring occurs in the direction in which the plate has the lowest shape rigidity the deformation becomes relatively large. The original square plate thus obtains after the compression moulding a rhombic shape. Such a rhombic shape leads to poor pattern fitting of the adjacent plates in the complete plate package, which in turn leads to lower pressure strength of the plate package.